One electrophotographic type color printer conventionally well known in the art includes four photosensitive drums and four developing rollers. The photosensitive drums are provided in correspondence with colors of yellow, magenta, cyan, and black, respectively. The developing rollers are provided in one to one correspondence with the photosensitive drums and are designed to supply toner to the photosensitive drums.
As one example of such a type of printer, there is known a laser printer that includes an image formation unit frame and a plurality of developing cartridges. The image formation unit frame integrally supports a plurality of photosensitive drums in correspondence with a plurality of colors such that the photosensitive drums are incapable of being detached from the image formation unit frame. The image formation unit frame can be pulled out of the main casing of the laser printer and detached from the main casing. Each developing cartridge is detachably mounted to the image formation unit frame in correspondence with one of the photosensitive drums.